The present invention relates to a device for controlling at least one gas-changing valve of an internal combustion engine.
A known device of this type (DE 198 26 047 A1) has as a valve adjuster or as an actor or actuator a double-action, hydraulic working cylinder, in which an adjusting piston is axially and displaceably guided, which is fixedly connected with the valve shaft of the gas-changing valve integration in the combustion cylinder or itself, forms its end remote from the valve-closing member. The adjusting piston defines a lower and upper pressure chamber in the working cylinder with both of its front faces turned from one another. The lower pressure chamber, via which a piston displacement in the direction of the valve closing is affected, is constantly acted upon by pressurized fluid. The upper chamber, which has a supply and return, via which a piston displacement in the direction of the valve opening is affected, is acted upon by pressurized fluid via the supply, or via the return, is again released to the approximate ambient pressure with the assistance of control valves, preferably 2/2 way magnet valves. The pressurized fluid is run from a regulated pressure supply. Of the control valves, a first control valve connects the second pressure chamber with the pressure supply and a second control valve connected the upper pressure chamber with a release line opening into a fluid reservoir. In the closed state of the gas-changing valve, the upper pressure chamber is separated by the closed first control valve from the pressure supply and is connected with the release line by the opened second control valve, so that the adjusting piston is transported by the prevailing fluid pressure in the lower pressure chamber into its closed position. For opening of the gas-changing valve, the control valves are actuated, whereby the upper pressure chamber is locked from the release line and is connected to the pressure supply. The gas-exchange valve opens, since the active surface of the adjusting piston is greater in the upper pressure chamber than the active surface of the adjusting piston in the lower chamber, whereby the size of the opening stroke depends on the form of the electrical control signal on the first control valve and the opening speed of the fluid pressure controlled from the pressure supply. For closing of the gas-changing valve, the control valves again switch. Thereby, the locked upper pressure chamber opposite the pressure supply lies on the release line, and the fluid pressure prevailing in the lower pressure chamber guides the adjusting piston back into its upper end position, so that the gas-changing valve is closed by the adjusting piston.
With such a device, the requirements exist of a fast closing of the gas-changing valve and, simultaneously, a minimal striking velocity of the valve closing member on the valve seat, which, from threshold values determined on noise and wear grounds, may not be exceeded.
In this connection, it has already been proposed (DE 102 01 176.2) to use a valve brake, which is coupled with the valve closing member of the gas-changing valve or with the valve adjuster. The valve brake, which is active during a remaining closing stroke of the valve closing member, has a hydraulic damping member with a fluid displacement volume flowing off via an opening cross section of a throttle opening. In a form of the damping member integrated in the valve adjuster, the return of the upper pressure chamber is separated into two run-off openings connected to one another and arranged axially spaced in the housing, from which the upper run-off opening is associated with a restrictor and the lower run-off opening is position in the displacement path of the adjusting piston, such that it is displaceable from this before reaching the upper end position. The opening cross section of the throttle opening of the restrictor is adjusted with a pressure-controlled throttle. Its control pressure is adjusted by means of an electrically controlled, hydraulic pressure valve and an electronic control apparatus that controls the pressure valve in dependence on the viscosity of the displacement volume. This has the advantage that the valve closing member, moved in the closing direction of the gas-changing valve quickly by the valve adjuster is abruptly braked shortly before reaching the closing position of the gas-changing valve, whereby the braking action is independent from the temperature and the viscosity of the fluid volume displaced over the throttle opening. Since the opening cross section of the throttle opening is reduced with increasing temperature, and therewith, lowered viscosity by the control, the flow speed of the displaced fluid volume is reduced through the throttle opening, so that the amplitude of the braking of the adjusting piston by the damping member remains approximately constantly independent from the instantaneous viscosity of the fluid volume. For adjustment of the throttle opening, the output signal of a temperature sensor that measures the temperature of the fluid displacement volume is supplied to the electronic control apparatus that controls the hydraulic pressure regulating valve. In the control apparatus, a first characteristic line providing the functional connection between the opening cross section of the restrictor and the hydraulic control pressure on the throttle member, a second characteristic line providing the functional connection between viscosity and hydraulic control pressure, as well as a third characteristic line providing the functional dependent of the viscosity of the temperature are stored. From these three characteristic lines, the control signal for the hydraulic pressure is derived in dependent on the measuring signal of the temperature sensor.
The device of the present invention for controlling at least one gas-changing valve of an internal combustion engine has the advantage that the control pressure for adjusting of the opening cross section of the throttle opening for the purpose of maintenance of a constant flow speed, which is independent from the viscosity of the fluid, of the fluid volume displaced from the upper pressure chamber with the assistance of a temperature-dependent actor, for example, an elastic-material element, bimetal, or the like, is directly generated in dependent on the temperature. In this manner, no expensive, electronic control apparatus and no electrical cabling is required. The pressure-regulating valve that is temperature-controlled from the actor is adjusted with the opening cross section of the throttle opening, such that a desired dependency of the opening cross section from the fluid temperature is achieved.